The invention relates generally to suspension locking of work vehicles. More particularly it relates to automatic suspension locking of skid steer vehicles when the operator manipulates a manual input device.
Skid steer loaders are small highly maneuverable vehicles that are used in place of front end loaders, backhoes and the like in constricted environments. They are particularly useful due to their small size and maneuverability.
Their maneuverability is due to their method of steering. The wheels on one side of the vehicle (typically two) can be driven independently of the wheels on the other side of the vehicle. The wheels themselves are not steerable. In other words, they cannot be turned about a generally vertical axis with respect to the chassis.
To steer a skid steer vehicle, the wheels on one side of the vehicle are driven at a different speed than the wheels on the other side of the vehicle. In an extreme case they are also driven in opposite directions. Thus, the wheels on one side can be driven forward as the wheels on the other side of the chassis are driven in reverse.
These different velocities (and/or different directions) cause the wheels to skid sideways as they rotate. As a result, one side of the vehicle advances faster than the other, and the vehicle turns. In the extreme case, when the wheels on either side are driven in opposite directions, the vehicle can rotate about a vertical axis within the perimeter of the vehicle""s chassis thereby giving it a turning radius of zero.
In addition to the maneuverability provided by the steering arrangement, skid steer vehicles also benefit from a narrow wheelbase and small width over wheels. A short wheelbase and small width over wheels permits the vehicle to be used in confined spaces, but prevents the use of sprung suspensions.
A sprung suspension used on a short wheelbase vehicle would cause excessive diving as the implement connected to the loader arms is used to engage the ground. When the bucket or other implement mounted on the loader arms of the skid steer vehicle are pressed downward against the ground or are used to lift an object or a load of dirt (for example) the forces generated by engagement with the ground could cause a short wheelbase vehicle such as a skid steer loader to pitch up and down precipitously.
For this reason, skid steer vehicles having a short wheelbase (such as the common skid steer loader) have never been equipped with sprung suspensions.
Sprung suspensions for skid steer vehicles would be desirable if they could be locked at the operator""s command. In this manner, the operator can directly control the suspensions to simulate a traditional un-sprung skid steer vehicle whenever he desires thereby reducing or eliminating the pitching on operator command. It is an object of this invention to provide a skid steer vehicle having such an operator control.
Even more advantageously, it would be desirable to provide a system that the operator can lock and unlock without requiring him to remove his hands from existing controls used to move the vehicle, to lift and lower the loader arms or to tilt the bucket. It is another object of this invention to provide a skid steer vehicle having such an operator control.
In accordance with a first embodiment of the invention, a skid steer vehicle having a system for manually locking a plurality of sprung suspensions is provided, the vehicle including a chassis having a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; four control arms pivotally coupled to the chassis and coupled to the four wheels to permit the wheels to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; four hydraulic cylinders, each cylinder operably coupled to one of the wheels to control at least the vertical position of the wheels with respect to the chassis; a set of manually-actuable operator controls including at least a first operator-actuable control configured to signal a desired wheel rotation, and at least a second operator-actuable control configured to signal a desired movement of the at least one loader arm; a manually-actuable operator input device configured to generate a signal indicative of a request for suspension locking; and an electronic controller operably coupled to the set of manually-actuable operator controls, the manually-actuable operator input device, the first and second pumps, and the at least one hydraulic cylinder to vary the displacement of the first and second pumps in response to manipulation of the first operator-actuable control, to fill the at least one hydraulic cylinder in response to manipulation of the second operator-actuable control, and to lock the four wheels in a vertical position with respect to the chassis in response to manipulation of the manually-actuable operator input device.
The manually-actuable operator input device may be fixed to at least one of the operator actuable controls of the set of manually-actuable operator controls such that the operator can simultaneously manipulate both the manually-actuable operator input device and said at least one of the operator-actuable controls with the same hand. The at least one of the operator-actuable controls may be a joystick, and the manually-actuable operator input device may be a switch mounted on that joystick. The skid steer loader of claim 3, further comprising four valves, each of the four valves being coupled to one of the four hydraulic cylinders to control an outflow of fluid from one of the four hydraulic cylinders. The vehicle may include four gas-charged hydraulic accumulators, each accumulator coupled to and between one of the valves and the one of the valves"" associated cylinder to block hydraulic fluid flow from the associated cylinder to said each accumulator. The electronic controller may be configured to lock the wheels with respect to the chassis by closing the four valves when the operator manipulates the manually-actuable operator input device. The manually-actuable operator input device may be a momentary contact switch.
In accordance with a second embodiment of the invention, a skid steer vehicle is provided having a chassis with a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel of the four wheels to permit the associated forward wheel to pivot in at least a vertical direction with respect to the chassis; at least two hydraulic motors for driving the four wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels of the four wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis; a set of manually-actuable operator controls including at least a first operator-actuable control configured to signal a desired wheel rotation, and at least a second operator-actuable control configured to signal a desired movement of the at least one loader arm; a manually-actuable operator input device configured to generate a signal indicative of a request for suspension locking; an electronic controller operably coupled to the set of manually-actuable operator controls, the manually-actuable operator input device, the first and second pumps, and the at least one hydraulic cylinder, to vary the displacement of the first and second pumps in response to manipulation of the first operator-actuable control, to fill the at least one hydraulic cylinder in response to manipulation of the second operator-actuable control, and to lock the two forward wheels in a vertical position with respect to the chassis in response to manipulation of the manually-actuable operator input device.
The manually-actuable operator input device may be fixed to at least one of the operator actuable controls of the set of manually-actuable operator controls such that the operator can simultaneously manipulate both the manually-actuable operator input device and said at least one of the operator-actuable controls with the same hand. At least one of the operator-actuable controls may include a joystick, and the manually-actuable operator input device may be a switch mounted on the joystick. The skid steer vehicle may further include two valves, each of the two valves being fluidly coupled to one of the two hydraulic cylinders to control an outflow of fluid from said one of the two hydraulic cylinders. The vehicle may also include two gas-charged hydraulic accumulators, wherein each accumulator is fluidly coupled to and between one of the two valves and said one of the two valves"" associated cylinder to block hydraulic fluid flow from the associated cylinder to said each accumulator. The electronic controller may be configured to lock the wheels with respect to the chassis by closing the two valves when the operator manipulates the manually-actuable operator input device, and further wherein the manually-actuable operator input device is a momentary contact switch.
In accordance with a third embodiment of the invention, a method of manually locking the suspensions of a skid steer vehicle is provided, the vehicle including a chassis having a left side and a right side, at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis, at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis, an engine coupled to the chassis, first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure, four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation, two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel of the four wheels to permit the associated forward wheel to pivot in at least a vertical direction with respect to the chassis, at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis, two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels of the four wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis, a set of manually-actuable operator controls including at least a first operator-actuable control configured to signal a desired wheel rotation, and at least a second operator-actuable control configured to signal a desired movement of the at least one loader arm, a manually-actuable operator input device configured to generate a signal indicative of a request for suspension locking, and an electronic controller operably coupled to the set of manually-actuable operator controls, the manually-actuable operator input device, the first and second pumps, and the at least one hydraulic cylinder to vary the displacement of the first and second pumps in response to manipulation of the first operator-actuable control, to fill the at least one hydraulic cylinder in response to manipulation of the second operator-actuable control, and to lock the two forward wheels in a vertical position with respect to the chassis in response to manipulation of the manually-actuable operator input device, the method comprising the steps of manipulating the manually-actuable operator input device to generate a locking command indicative of a wheel locking request; receiving the locking command in the electronic controller; and locking the two forward wheels to prevent vertical motion of the two forward wheels with respect to the chassis in response to receipt of the locking command in the electronic controller.
The step of manipulating may include the step of pressing a switch. The vehicle may further comprise two valves, wherein each of the two valves is fluidly coupled to an associated one of the two hydraulic cylinders to control the outflow of fluid from said associated one of the two hydraulic cylinders, and further wherein each of said two valves is operably coupled to the electronic controller to be closed thereby in response to the step of pressing the switch. The switch may be disposed on one of the first or second operator-actuable controls. The first and second operator-actuable controls may be joysticks. The method may also include the steps of manipulating the manually-actuable operator input device to generate an unlocking command indicative of a wheel unlocking request; receiving the unlocking command in the electronic controller; and unlocking the two forward wheels of the four wheels to permit vertical motion of the two forward wheels with respect to the chassis in response to receipt of the unlocking command in the electronic controller. The manually actuable operator input device may be a switch, and the step of manipulating to generate the locking command may include the step of pressing the switch, and the step of manipulating to generate an unlocking command may include the step of releasing the switch